Spacewalk success! NASA astronauts ahead of schedule on ISS repairs

Deborah Netburn

The first in a series of emergency spacewalks to fix a cooling system failure on the International Space Station went off without a hitch Saturday morning.

In fact, it went so well that the two spacewalkers, NASA astronauts Rick Mastracchio and Michael Hopkins, were able to get a headstart on some of the tasks planned for their next spacewalk scheduled for Monday.

The emergency spacewalks were arranged last week to fix a problem with a pump in one of the space station's two external ammonia cooling loops that help keep instruments both inside and outside the station from overheating.

The space station uses ammonia in its external cooling loops, but it’s far too toxic to use in the loops inside the station; the internal ones use water instead. But if the ammonia gets too cold, it could freeze the water from the internal system in its pipes. As the water turns into ice, it expands and could crack the pipes, allowing ammonia to enter and poison the system.

After manipulating a problematic valve for several days to see if they could find a solution, NASA officials made the decision to send Mastracchio and Hopkins out into space to replace the refrigerator-sized pump with one of three spares located outside the space station.

Saturday's spacewalk was the first of three planned to remove and replace the pump. The other two are scheduled for Monday and Wednesday. However, Mastracchio and Hopkins were so efficient that the agency said the final spacewalk on Christmas Day may not be necessary.

Saturday's spacewalk began at 4:01 a.m. PST and lasted five hours and 28 minutes -- about one hour less than NASA had originally anticipated. With Mastracchio attached to the end of the ISS's 57-foot robotic arm, the two astronauts disconnected four ammonia fluid lines from the pump module and attached them to a pump module jumper box that will help keep the ammonia in a liquid state.

Since they were so far ahead of schedule, Mission Control in Houston told the two astronauts to go ahead and tackle the first of Monday's tasks -- removing the old pump module and storing it temporarily out of the way.

In the photo gallery above you can see Mastracchio holding the 780-pound pump as flight engineer Koichi Wakata inside the space station guides the robotic arm into place.